There is currently a high degree of activity throughout the pulp and paper industry in the recycling of paper products, and it is therefore important that this industry be provided with the most efficient systems and methods for deinking and otherwise cleaning and preparing waste paper for reuse.
It has been proposed as one approach to this objective that prior to treatment of waste paper stock to remove dispersed ink and other small contaminant particles therefrom, which is commonly done by froth flotation, the stock be fractionated into a long fiber fraction and a fines fraction which also includes the ink and other small particles. The two fractions can then be treated separately in subsequent cleaning and bleaching operations before being recombined for final preparation and reuse in the making of paper. A practical problem in utilizing this procedure has been difficulty in minimizing the extent to which long fibers remain in the fines fraction, because they tend both to interfere with removal of the small contaminant particles and also to be removed with those particles.